Detailed descriptions of mobile communication networks and systems can be found in the literature, such as in particular Technical Specifications published by standardisation bodies such as for example 3GPP (3rd Generation Partnership Project).
In such systems, a mobile terminal or User Equipment (UE) has access to mobile services (such as in particular IP-based mobile services) via an Access Network (such as in particular packet-based Access Network) comprising a Radio Access Network (RAN) and a Core Network (CN).
Examples of 3GPP-based mobile communication systems include 2G GSM/GPRS, 3G UMTS, LTE also known as EPS (Evolved Packet System). Examples of Radio Access Network (RAN) include GERAN (for 2G GSM/GPRS), UTRAN (for 3G UMTS), E-UTRAN (for LTE). Examples of packet Core Network include GPRS Core (for 2G or 3G) and Evolved Packet Core EPC (for 2G, 3G UTRAN and LTE).
For example, EPS architecture is recalled in FIG. 1, taken from 3GPP TS 23.401. Within EPS, EPC may be accessed via E-UTRAN or via UTRAN/GERAN. EPC comprises entities such as MME (Mobility Management Entity), SGSN (Serving GPRS Support Node) supporting an S4 interface to a SGW and thus called S4-SGSN, SGW (Serving Gateway) and PGW (Packet Data Network PDN Gateway). MME interfaces with E-UTRAN in the control plane via S1-MME interface. S4-SGSN interfaces with UTRAN/GERAN in the control plane via the Iu/Gb interface respectively. SGW interfaces with MME/S4-SGSN in the control plane via S11/S4 interface respectively. SGW interfaces with E-UTRAN in the user plane via S1-U interface. SGW interfaces with UTRAN in the user plane via S12 interface. SGW interfaces with PGW in the user plane via S5/S8 interface.